1. Field of the Invention
This invention relates to a silver halide photographic material containing a photographic tanning developing agent and, more particularly, to a silver halide photographic material containing a polyhydroxy-spiro-bis-chroman developing agent and a gallic acid alkyl ester.
2. Description of the Prior Art
In general, catechol, hydroquinone, pyrogallol, etc., have been known for a long time as so-called tanning developing agents which act as strong developing agents for photosensitive silver halides and form oxidation products which react with gelatin to tan it strongly. It has also been widely known to use these tanning developing agents in photographic emulsions or developers as disclosed in U.S. Pat. No. 2,592,368. In the case of using tanning developing agents in developers, it is sometimes more difficult to obtain images having excellent sharpness as compared to when using tanning developing agents in photographic emulsion layers because the tanning developing agents are more likely to diffuse and move through silver halide emulsion layers during development. The image density obtained when the tanning developing agents are in developers is less as compared to the latter case because the developing agents do not act sufficiently and hence tanning of image areas is incomplete. As a result the tanned image areas are partially dissolved in subsequent processing steps. Consequently, it is generally preferred, in obtaining so-called wash-off relief images, to incorporate tanning developing agents in photographic materials rather than in the developers.
When water-soluble tanning developing agents such as pyrogallol and hydroquinone are incorporated in silver halide emulsion layers or layers adjacent thereto, the developing agents tend to have an undesirable effect on photographic properties. They may cause fogging upon storage of the photographic materials for a long period of time, a reduction in image density upon development as a result of a reduction in developing activity, and insufficient tanning. Also, when photographic materials prepared by coating a support with a silver halide photographic emulsion containing a tanning developing agent are processed with an alkaline aqueous solution after light exposure, sometimes the developing agent is quickly lost in the alkaline solution and hence a suitable silver density and sufficiently tanned images are not obtained.
Furthermore, because most tanning developing agents diffuse through coated gelatin layers, they can cause tanning of non-image areas. Therefore, to obtain preferred wash-off relief images with good photographic properties, tanning developing agents which have a strong developing activity, the oxidation products of which have a good tanning property, and which are stable for a long period of time when added to silver halide emulsions are needed. Moreover, to prevent tanning non-exposed areas, the diffusion speed of the developing agents in gelatin layers or gelatino silver halide emulsion layers should not be too high.
U.S. Pat. No. 2,751,295 discloses that 6,7,6',7'-tetrahydroxy-4,4,4',4'-tetramethyl-bis-2,2'-spiro-chroman which is a compound of formula (I) of the present invention is a tanning developing agent. However, the U.S. patent says only that the compound does not exhibit the preferred properties of catechol derivatives. In more detail, the patent does not teach the use of the spiro-chroman compound with the gallic acid ester of formula (II) as in this invention nor does it suggest that the objects of this invention can be obtained by using a spiro-chroman of formula (I) and the gallic acid ester of formula (II) in combination.
U.S. Pat. No. 3,440,049 discloses that a polyhydroxy-spiro-bis-indane compound can be used together with the compound of formula (II) but the polyhydroxyspiro-bis-indane compound is quite different from the compounds of formula (I), and it is clear that the combination described in that patent is different than the combination of the present invention. Furthermore, the use of the indane compound sometimes gives rise to insufficient image density and the compound is not easily prepared or readily available. One of the characteristic features of this invention is that it overcomes the defects of conventional tanning developing agents such as the polyhydroxyspiro-bis-indane compound and catechol.
Furthermore, U.S. Pat. No. 3,453,109 discloses that a 4-substituted-3-pyrazolidone compound and gallic acid can be used as developing agents for obtaining relief images. However, the patent neither discloses the use of gallic acid and the compounds of formula (I) in this invention nor does it teach the use of the gallic acid esters of formula (II) which are characteristic of this invention. On the other hand, the present invention does not use the compound of formula (II) and the 4-substituted-3-pyrazolidone compound without the compound of formula (I). That is, the present invention is based on the discovery that when the compound of formula (I) is used together with the compound of formula (II), excellent results which are not expected based on conventional knowledge are obtained.